Cellular networks were originally developed to provide primarily voice services over circuit switched (CS) networks. However, the introduction of packet switched (PS) networks enables network operators to provide data services as well as voice services to users. Eventually, network architecture is expected to evolve toward all-IP networks capable of providing both voice and data services.
Currently, some UEs implement functionality that allows them to transition from communicating with a PS network, e.g., via an LTE network, to communicating with a CS network, e.g., via IS95/CDMA network. To accomplish this, the UEs enter an idle mode with respect to the CS network after registering with the CS network, and begin communicating over the PS network. While the UE is in the CS network idle mode, the CS network may provide the UE with services notifications. For example, the CS network may alert the UE to an incoming call. Additionally, the UE may autonomously transition from the PS network to the CS network for a short period of time to perform some function associated with a CS network idle mode, or more specifically, some function associated with the Radio Resource Control (RRC) idle mode associated with the RAN that connects the UE to the CS network, such as to read a paging channel, check paging notifications for incoming calls, or perform a location update procedure. Once the CS operations are complete, the UE returns to the CS network idle mode and transitions back to communicating in the PS network.
Some UEs have two or more receivers, and thus, can maintain connections to both the CS and PS networks. However, not all UEs can establish and maintain two different connections. Particularly, some UEs have only a single transceiver, and thus, must temporarily “tune-out” of one network, e.g., the PS network, to communicate with the other, e.g., the CS network. For a UE, “tuning out” of the PS network can be problematic, particularly if there is data in the downlink buffers. More specifically, a UE would have to tune-out of the PS network for up to two seconds to perform a task, and therefore would risk being dropped by the PS network.
Those UEs having dual receivers, however, may be simultaneously connected to both an LTE network for PS services, and a CS network, e.g., a CDMA 1XRTT network, for CS services. This may be accomplished using a first receiver chain in the UE to monitor the LTE network, or the PS network via the LTE network, and a second receiver chain in the UE to monitor the CS network. With dual receivers, a UE in idle mode in both the LTE/PS and CS networks is able to perform idle mode cell reselection and page monitoring independently in both networks at the same time. Thus, a UE having dual receivers functions more or less as one LTE UE and one CDMA UE combined together.
However, when the UE is operating in Carrier Aggregation (CA) mode in the PS network, i.e., the UE is configured with one or more secondary serving cells, the UE may not be able to simultaneously monitor the CS network and all of its serving cells, i.e., its Primary serving Cell (PCell) and Secondary serving Cells (SCells), in the PS network. In such cases, the second receiver chain of the UE would have to be shared between the CS network and the one or more secondary serving cells also using the receiver. The UE would therefore need to “tune-out” on one or more secondary serving cells of the PS network in order to perform a task in the CS network.
A UE having dual receivers may perform an LTE access upon being paged by the CS network. The access serves to inform the LTE network of the page received from the CS network, and that the UE may be unreachable by the LTE network while it is connected to the CS network. One method for performing this access function is defined in chapter 10.3 of version 10.3.0 of the Third Generation Partnership Project (3GPP) Technical Specification (TS) 36.300 entitled, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 10),” published March 2011.
Although both single and multiple transceiver UEs can “tune-out” of a network, conventional methods do not define a solution that functions for both types of UEs—i.e., single transceiver and dual or multiple transceiver UEs. For example, one potential solution for dealing with the problems associated with tuning-out of a secondary cell is provided in 3GPP TSG-RAN WG2 #77 R2-120306. The solution defined therein, however, is for dual-transceiver UEs and does not consider situations in which the UE tunes-out completely, such as would be the case of a single receiver UE tuning out of a Primary Cell (PCell), also denoted Primary serving Cell, in a non-carrier aggregation (CA) configuration. This means that two separate solutions are needed—one solution for CA configured UEs, and another solution for non-CA configured UEs.